The present invention relates to distribution of liquid droplets on a layer of filamentary material, and more particularly to improvements in apparatus for applying liquid plasticizer to a running tow of filamentary material, especially filamentary filter material which can be used for the manufacture of filter mouthpieces for cigarettes, cigars or cigarillos. Still more particularly, the invention relates to improvements in apparatus for applying minute droplets of atomized liquid plasticizer (such as triacetin) on a spread out layer or tow of filaments which may constitute cellulose acetate fibers of the type often employed in the manufacture of fillers for filter rod sections which are thereupon subdivided into filter mouthpieces of desired length.
It is already known to propel finely atomized liquid plasticizer against one side of a running tow of filamentary filter material. For example, U.S. Pat. No. 3,387,992 granted June 11, 1968 to Arthur et al. discloses a process and apparatus for propelling droplets of liquid plasticizer against the underside of a running tow of filamentary material by resorting to a hollow disc having several peripheral outlets. Liquid plasticizer is fed into the disc and is propelled through the outlets and against the running tow under the action of centrifugal force. The droplets which penetrate through the normally permeable spread out tow descend onto the upper side of the tow by gravity. The patent to Arthur et al. further discloses the possibility of using two hollow discs, one at each side of the running tow, when the tow is relatively dense or is non-porous or impervious to such an extent as to prevent droplets issuing from a single disc from passing through the material of the tow. Neither of the two proposals insures satisfactory (uniform) application of plasticizer, i.e., such application that each and every increment or unit length of the running tow retains a fixed quantity of atomized plasticizer.
Commonly owned British Pat. No. 1,392,063 discloses a modified apparatus wherein a nozzle sprays liquid plasticizer against one side of the running tow and the other side of the tow slides along a stationary plate so that all droplets which penetrate through the tow are intercepted by the plate and are swept away by the filaments of the tow. Such apparatus insures more satisfactory distribution of plasticizer in successive unit lengths of the tow; however, its application in filter rod making or like machines is limited due to the fact that certain types of filamentary material cannot withstand continuous rubbing against a stationary surface.